Hey guys, how do you make friends in your mid-20s after you're done with college but don't have kids and don't have any new hobbies?

I'm not really looking for a lot of friends, because I'm introverted and not a huge people-person. But it would be nice to have one or two more good friends. I'm involved in martial arts and have lots of friends there, but none are super close friends (and that's ok). The only other thing I do is swim laps, which is kind of a solo thing. I guess I could try at work (I'm a grad student), but I just don't even know where one starts making friends outside of schoolin'. A fantastic trio of devious friendship involving shenanigans and drink fancy beverages and laughing at eutie when she rambles on about plant pathogens in agriculture would be ideal.

Anyone have any fabulous stories of meeting lovely people post-college that ended up being permanent life fixtures? Give me hope!